Ghrelin: All about the hunger hormone

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Ghrelin is a hormone mainly produced in the stomach when it is empty. It is also produced in the small intestine, brain, and pancreas.
Ghrelin
Ghrelin travels through the bloodstream to the brain, where it acts on the hypothalamus. The hypothalamus is a part of the brain, which produces hormones that regulate hunger, mood, thirst, and many other important functions within the body.
hypothalamus
Ghrelin is often referred to as the hunger hormone because its primary role is to regulate appetite. When ghrelin activates its receptor — growth hormone secretagogue receptor — it causes a person to eat more food and store extra fat.
causes
In people who are trying to lose weight or who have recently lost weight, ghrelin levels are often higher, making it challenging to maintain weight loss.
For example, one study from 2020 looked at people with diabetes who participated in a 2-year weight management program. Participants who initially lost weight slowly regained it over the study duration. Researchers found that weight loss was associated with increased ghrelin levels and increased hunger, which might make it difficult to keep weight off.
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diabetes
Ghrelin can also signal the body to decrease brown fat thermogenesis. When this happens, the body burns less fat at rest. Brown fat is known for its thermogenic properties and ability to increase overall calories burned.
decrease brown fat thermogenesis
thermogenic properties
calories
Studies show that ghrelin also affects a person’s sleep/wake cycle, taste sensation, and reward-seeking behavior.
affects
As it plays a role in reward processing, many experts believe higher ghrelin levels can contribute to food and alcohol misuse.
experts
Recently, researchers have discovered that ghrelin also has many functions in the body, including improving heart health, preventing muscle atrophy, and influencing bone metabolism.
researchers
muscle atrophy
It can also stimulate gastric acid secretion and accelerate gastric emptying.
accelerate gastric emptying
What causes ghrelin levels to rise?
Levels of ghrelin frequently change throughout the day and are primarily controlled by food intake. Ghrelin levels usually rise when the stomach is empty and decrease once a person has eaten.
Ghrelin levels
Some studies show that people who have obesity have higher levels of ghrelin circulating. This can lead to a continuous state of hunger and make it difficult to lose weight.
studies
However, research remains conflicted on this point. Yet a 2015 review suggests that ghrelin levels are low in people with obesity and even lower in people with obesity who also have a binge-eating disorder.
2015 review
obesity
binge-eating disorder
Dieting also has been known to stimulate ghrelin secretion. What is more, diets can also decrease leptin levels, which is known as the “satiety hormone.” Combined, this may make it difficult to lose weight and keep it off long term.
Dieting
decrease
Interestingly, experts believe people who have undergone weight loss surgery have lower levels of ghrelin, which may make it easier to keep weight off.
In particular, one recent review found that ghrelin levels fall significantly following sleeve gastrectomy. Researchers believe this is because part of the stomach — the gastric fundus — where most ghrelin is produced is completely removed. However, the results of other studies are inconsistent for other weight loss procedures such as roux-en-y gastric bypass.
review
roux-en-y gastric bypass
People with certain health conditions also tend to have elevated ghrelin levels.
People with obesity and Prader-Willi syndrome (PWS) have very high levels of ghrelin circulating, which may play a role in their constant sense of hunger and difficulty controlling weight.
Prader-Willi syndrome (PWS)
Additionally, people with Hashimoto’s thyroiditis, anorexia nervosa, bulimia, and cachexia from illness tend to have higher hunger hormone levels.
Hashimoto’s thyroiditis
anorexia nervosa
bulimia
cachexia
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Ghrelin levels also may be higher during periods of stress. Higher ghrelin levels are thought to have an anxiolytic effect on the body.
anxiolytic
How to increase ghrelin levels
Although elevated ghrelin levels are commonly perceived as unfavorable and associated with increased appetite, certain individuals may benefit from higher ghrelin levels.
For instance, someone struggling to gain weight or with wasting syndrome may benefit from the appetite-stimulating effects of ghrelin.
Newer studies suggest ghrelin administration may potentially be helpful in patients with cancer cachexia because it can help reverse weight loss and protein breakdown in catabolic states. Although short-term ghrelin administration appears to be safe and well-tolerated, we need more studies on its effectiveness and safety before recommending it.
studies
cancer
Animal research on how cannabis increases appetite by stimulating ghrelin production also appears to be promising to support its use in treating illness-induced anorexia.
Animal research
Additionally, one human study in men with HIV found that tetrahydrocannabinol (THC), the psychoactive compound in cannabis, can stimulate ghrelin release.
human study
HIV
How to decrease ghrelin levels
Ghrelin levels may increase following weight loss. Decreasing levels of ghrelin in the body may help decrease a person’s appetite, prevent weight regain, or promote weight loss.
increase
decrease a person’s appetite
However, it is important to note that other studies highlight monitoring changes in ghrelin alone are not sufficient to predict weight gain following weight loss in most people. Behavioral, physiological, and environmental factors also play a role in weight regain.
studies
A person who wants to naturally decrease ghrelin levels may want to try some of the following interventions.
People’s ghrelin levels tend to increase when on a diet and not eating enough calories. Avoiding an empty stomach and eating a nutrient-rich diet may help limit ghrelin secretion.
According to the Dietary Guidelines for Americans, 2020–2025, the main elements that make up a healthy dietary pattern include:
Dietary Guidelines for Americans, 2020–2025
vegetables of all types
fruits, especially whole fruit
grains, at least which half are whole grains
low fat dairy
lean protein
oils, such as olive oil and those naturally occurring in nuts and fatty fish
Some foods may also decrease ghrelin levels. In one older study, researchers discovered that fiber-rich foods could reduce ghrelin levels.
study
Another study looked at 21 men who were either given a bagel or eggs for breakfast. The group who ate eggs for breakfast had decreased ghrelin levels than those who ate bagels.
study
Poor sleep patterns are tied to increased ghrelin levels and decreased leptin levels, leading to increased appetite and hunger. For better sleep, aim to get a minimum of 7 hours of sleep in a 24-hour period.
increased ghrelin levels
7 hours of sleep
Consuming high protein meals and snacks can help promote satiety and reduce ghrelin levels. In fact, many meal-related studies have shown significant reductions in hunger and increased fullness following high protein meals.
help promote satiety
Researchers suggest getting between 1.2-1.6 grams of protein per kilogram of body weight per day or 25–30% of daily calories to promote weight management and appetite suppression. Most people can follow a high protein diet by eating chicken breast, beans, lentils, low fat dairy, and shellfish.
Researchers
body weight
Although removing stress altogether is near impossible, studies show that high levels of chronic stress can lead to elevated ghrelin levels. In addition to signaling hunger, ghrelin may affect brain function. The exact mechanism remains unclear, and mixed findings make it difficult to draw conclusions about ghrelin’s role in stress.
stress
high levels of chronic stress
Some animal studies suggest it may reduce anxiety and have antidepressant-like properties, while other studies suggest it may promote these behaviors.
animal studies
anxiety
antidepressant
Regular physical activity, adequate sleep, and practicing yoga or meditation can help minimize stress.
yoga
Research surrounding the effect of exercise on ghrelin levels remains conflicting. In one 2021 review, researchers found that acute exercise suppresses ghrelin production. However, they also found that long-term exercise programs may have the opposite effect and increase ghrelin production.
2021 review
The exact mechanism behind these effects remains unclear, but researchers believe it is likely due to elevated blood flow redistribution and weight loss from exercise.
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Summary
Ghrelin is known as the hunger hormone due to its key role in appetite regulation. High levels of ghrelin lead to an increase in appetite and food intake. However, the body needs ghrelin because it is involved in many processes. These include improving heart health, influencing bone metabolism, and preventing muscle breakdown.
A person who wishes to naturally reduce ghrelin levels in the body may consider eating a healthy, fiber-rich diet, consuming adequate protein, exercising, getting enough sleep, and minimizing stress.
In contrast, someone with illness-induced anorexia or difficulty gaining weight may benefit from higher ghrelin levels to promote hunger and weight gain.